Traditionally, connection terminals of circuit boards are connected to connection portions of other circuit boards or electronic devices, such as IC chips, via an anisotropic conductive adhesive film 43. As shown in FIG. 4(a), the anisotropic conductive adhesive film 43 is composed of a thermosetting resin 42 and conductive particles 41 dispersed in the thermosetting resin 42.
To improve the connection reliability of such anisotropic conductive adhesive film, the conductive particles have been required to be effectively confined between the connection terminals of a circuit board and the connection portions of an electronic device in making anisotropic conductive connection. To this requirement, a thin film shown in FIG. 4(b) is proposed which contains a greater number of the conductive particles than the film of FIG. 4(a), or a conductive particle-free, thermosetting adhesive layer 44 is laminated to a thin film shown in FIG. 4(c), which contains the same number of the conductive particles as the film of FIG. 4(a) but at a higher density, to make an anisotropic conductive adhesive film 43.
However, the constructions shown in FIG. 4 cannot effectively confine the conductive particles, and, thus, an attempt has been made to prevent the conductive particles from migrating from the connection area to the non-connection area during the thermocompression bonding for anisotropic connection. Specifically, this is done by making use of a technique described in Patent Document 1 for adjusting the melt viscosity of intercalated insulative adhesive-coated film. Using this technique, the resin composition of an entire anisotropic conductive adhesive film is adjusted to increase the melt viscosity of the film.
Patent Document 1: Japanese Patent Application Laid-Open No. 2000-104033